Drug paraphernalia seized by North Yorkshire police in a recent case.
Photograph: North Yorkshire police/PA

The UK is the largest host of fentanyl sales on the darknet in Europe, with 1,000 trades being made in the last few months, research shows.

Experts at the Oxford Internet Institute said the UK was a “significant player” in the trade of the synthetic opioid, a controlled class A drug that can be up to 100 times stronger than heroin. They warned that the drug was increasingly appearing on illicit websites.

A team at the institute has been scraping the world’s largest darknet marketplaces since April 2017. It found that the US accounts for almost 40% of global darknet trade, followed by Canada (15%) and Australia (12%). The largest seller in Europe is the UK (9%), followed by Germany, accounting for 5% of sales.

Joss Wright, a research fellow at the institute, said: “Why is the UK a significant player? … It’s because we have a relatively strong tech sector and users of the web, but also geographically the UK is quite well placed for trade coming from the US.”

He said that since data gathering began in April, there had been 4,850 trades in the US and about 1,000 in the UK.

Darknet markets or cryptomarkets have been operating since the launch of Silk Road in February 2011. On the darknet, those selling substances are able to remain relatively anonymous as their IP addresses are masked. People buy drugs using the online currency bitcoin.

Mark Graham, a professor of internet geography at the institute, said: “Many of the sellers in places like the US, Canada, and western Europe are likely intermediaries rather than producers themselves. While darknet marketplaces can, in theory, be accessed from anywhere in the world, our data suggests that there is often a local geography of trading. In other words, buyers tend to buy from domestic rather than international sellers.”

Two men were jailed last month for importing fentanyl and other class A drugs before selling them on the darknet. Ross Brennan, 29, from York, was sentenced to more than 13 years after making hundreds of thousands of pounds with 27-year-old Aarron Gledhill from Huddersfield, who was sentenced to just under four years for his part in the crime.

In what has been described as the first case of its kind in the UK because of their sophisticated use of technology, police searched Brennan’s property and found drugs with a street value of tens of thousands of pounds. They also seized a Chemistry for Dummies book, address labels, bags of cutting powder, a mixing machine, a microscope, a set of scales and packages from around the world.

The offences took place between 2013 and 2016. Between June and September 2015 alone, Brennan made 225 transactions using a dark website called AlphaBay, which has since been shut down.

Wright said fentanyl was appearing “more and more” on the dark web. “There has been a rise in the number of sales of that product … the darknet is a good place to buy things with extra guarantees of security and there is increasing trade there,” he said.

In response, some darknet marketplaces – including the drug market Hansa, which was shut down in July – had started banning fentanyl sales amid concerns it would attract too much attention from law enforcement, he said.

Judith Aldridge, a criminologist at the University of Manchester, said she would be surprised if sales of fentanyl did not increase. “Interestingly, over the past 12 months we’ve seen a demonisation of fentanyl, with many in the darknet community opposed to their sales on crypto-markets.”

Dr Andres Baravalle, from the University of East London, said research showed that 398 of 36,000 darknet adverts had mentioned fentanyl so far in 2017.

The Global Drug Survey 2017 said: “Despite disruptions from law enforcement efforts and scams, the size and scale of darknet markets for drugs continues to grow. At the time of the report there were over 20 functioning markets, according to dnstats.net.”

Graham, from the institute, said this had not deterred dealers. “Our research so far shows that shutting down these marketplaces has not reduced the total amount of trade. It’s a whack-a-mole game, so it is not reducing demand and supply … when you shut down one website another pops up. There is no indication it’s radically reducing demand or supply on these markets.”